1. Field of the Invention
The invention relates to an endoscope system capable of photographing tomographic images of a object inside a living body or the like, a scanning optical system suitable for use in such an endoscope system, and a polygon mirror suitable for use in such a scanning optical system. The present disclosure relates to subject matter contained in Japanese Patent Application No. Hei 11-225974 (filed on Aug. 10, 1999) which is expressly incorporated herein by reference in its entirety.
2. Description of the Prior Art
An endoscope system used for observing the interior of a patient""s body cavity has an endoscope to be inserted into the patient""s body cavity and an external unit connected to this endoscope. The external unit includes a light source section and a processor.
The endoscope has an elongate insertion tube to be inserted to the patient""s body cavity. The endoscope also has an illumination optical system, an objective optical system and a CCD. The illumination optical system, connected with the light source section in the external unit, illuminates an object (which is an inner wall of the body cavity) through an illuminating window provided at the distal end of the insertion tube. The objective optical system forms an image of the object through an observing window provided at the distal end of the insertion tube. The CCD is placed near an image-forming plane of the objective optical system, and connected to the processor in the external unit. Through the insertion tube is laid a forceps channel which is opened at the distal end of the insertion tube. Through the forceps channel, a forceps or various operative instruments are guided to the distal end of the insertion tube from the proximal end thereof.
By using such an endoscope system, the operator can observe the interior of a patient""s body cavity. More specifically, the operator inserts the endoscope into the patient""s body cavity, and illuminates a inner wall of body cavity through the illumination optical system. Then, the objective optical system forms the image of the inner wall of the body cavity onto a pick-up plane of the CCD surface. The CCD converts this image into image signals, and transmits the same to the processor in the external unit. The processor in the external unit then processes the received image signals of the inner wall of the body cavity to display the picture of the inner wall onto a monitor. In this state, the operator observes the interior of the patient""s body cavity, displayed on the monitor.
If finding a location having the possibility of cancer or a tumor through this observation, the operator inserts a forceps or a biopsy needle into the body cavity through the forceps channel of the endoscope so as to excise tissue from the location. Thus excised tissue is subjected to pathologic tests, and a diagnosis is given on the basis of the pathologic test results.
According to the conventional endoscope system of the above-described configuration, what is displayed as images is nothing but the surface of the inner wall of the patient""s body cavity. Therefore, biopsy is needed in order to know the condition of tissue under the surface of inner wall of the body cavity. In particular, biopsy is absolutely necessary for early detection of cancer, small tumors, and the like. Nevertheless, the pathologic tests on the tissue excised through the biopsy inevitably consume some time, resulting in a problem that the final diagnosis gets behind.
Moreover, with consideration given to the burden on the patient, the biopsy must be limited in area and in the number of times. Accordingly, simply administering pathologic tests not always promises an accurate diagnosis if lesions might also exist outside the operator-designated biopsy location.
An object of the present invention is to provide an endoscope system which makes it possible to give an accurate diagnosis in a short time. To achieve the foregoing object, an endoscope system according to the present invention comprises a first waveguide, a second waveguide, an optical coupler which optically couples these waveguides to each other, a low-coherent light source arranged on a proximal end of either one of the first and second waveguides and emits low-coherent light to be incident on this waveguide, a polygon mirror having a plurality of reflecting surfaces around its center axis, which differ from each other in tilt angle with respect to the center axis, a supporting mechanism which supports the polygon mirror and rotates it about the center axis, an incident optical member which guides low-coherent light emitted from a distal end of the first waveguide to a reflecting surface of the polygon mirror, an emission optical member which converges the low-coherent light reflected by the polygon mirror, a reflecting member which reflects low-coherent light emitted from a distal end of the second waveguide so that the low-coherent light returns into the second waveguide as reference light, optical path length adjusting mechanism which makes a relative change between length of an optical path extending from the optical coupler to an object through the first waveguide and that of another optical path extending from the optical coupler to the reflecting member through the second waveguide, a photodetector arranged on a proximal end of the other of the first waveguide and the second waveguide, which receives light from this waveguide, and signal processor generating a tomographic image of the object on the basis of a detection signal output from the photodetector while the optical path length adjusting mechanism makes the relative change and while the support mechanism rotates the polygon mirror.
In such a configuration, the low-coherent light emitted from the low-coherent light source is divided by the optical coupler in two, which are introduced through the first waveguide and the second waveguide, respectively. Low-coherent light emitted from the distal end of the first waveguide is guided through the incident optical system to a reflecting surface of the polygon mirror. The light is reflected by this reflecting surface onto the surface of the object. In this time, the polygon mirror is rotating about its rotary axis. The reflecting surfaces of this polygon mirror are different from each other in tilt angle with respect to the rotation axis. Therefore, the low-coherent light incident on the surface of the object forms a plurality of scanning lines shifted in parallel from each other corresponding to the individual reflecting surfaces of the polygon mirror. Thereby, the low-coherent light scans over a predetermined two-dimensional region on the object. Low-coherent light reflected by the object returns into the first waveguide as measurement light. Meanwhile, the low-coherent light that is halved by the optical coupler and introduced through the second waveguide is emitted out of the second waveguide, and reflected by the reflecting member. The low-coherent light reflected by the reflected member returns into the second waveguide as reference light. These measurement light and reference light interfere with each other in the optical coupler to make interference light, which the photodetector detects as a signal. In this time, the optical path length adjusting mechanism makes a change in optical path length, so that the signal processor can form a tomographic image concerning the three-dimensional region which is recognized as ranging from the two-dimensional region on the surface of the object to a predetermined depth under the surface.
The polygon mirror may be formed by tilting the individual lateral faces of a regular prism appropriately, or by tilting the individual lateral faces of a regular prismoid appropriately. The polygon mirror has e.g. six to twelve reflecting surfaces, whereas it may have any other number of reflecting surfaces.
The low-coherent light source may be a super-luminescent diode. This low-coherent light source may be arranged on the proximal end of the first waveguide with the photodetector on the proximal end of the second waveguide. Otherwise, the low-coherent light source may be arranged on the proximal end of the second waveguide in reverse, with the photodetector on the proximal end of the first waveguide.
A depthward scan at a certain scanning point on the surface of the object may be followed by a depthward scan at a next scanning point. Alternatively, a two-dimensional scan generally parallel to the surface of the object may first be performed with a fixed depthward scanning position, followed by the two-dimensional scan restarted with the depthward scanning position shifted.
Each of the waveguides may consist of a single-mode optical fiber, or be composed of a fiber bundle.
The optical coupler may be an optical fiber coupler, or a beam splitter composed of a prism and the like. In addition, the both waveguides and the optical coupler may have a property of polarization.
Moreover, the optical path length adjusting mechanism may be configured to move the reflecting member so as to approach or recede from the distal end of the second waveguide to change the length of the optical path from the optical coupler to the reflecting member via the second waveguide with respect to the optical path length from the optical coupler to the object via the first waveguide. A piezo element may be used as the mechanism for driving the reflecting member. A voice coil motor, a servomotor, or the like may be used instead thereof.
The optical path length adjusting mechanism may change the length of the optical path from the optical coupler to the object via the first waveguide while holding the reflecting member stationary. The reflecting member may be a mirror, a corner cube, or the like.
Furthermore, the endoscope system may be capable of ordinary observations and fluorescent observations.
The displaying means may be a CRT, a liquid crystal display, a plasma display, or the like.
A scanning optical system according to the present invention comprises a polygon mirror having a plurality of reflecting surf aces around its center axis, which differ from each other in tilt angle with respect to the center axis, a supporting mechanism which supports the polygon mirror and rotates it about the center axis, and an incident optical system fixed with respect to the supporting mechanism which introduces light toward the reflecting surfaces of the polygon mirror.
A polygon mirror according to the present invention has a plurality of reflecting surfaces around its center axis which differ from each other in tilt angle with respect to the center axis. This polygon mirror rotates about the center axis.